Another Bridge To Nowhere

I live a few miles from a bridge to nowhere. It was built a few miles from a centre of population. There was a bridge already at that place and another a few miles south. It cost $millions and is of questionable value. I’ve been over it a few times and it’s a lonely place. Usually there is not a single vehicle on it for long periods of time.

The bridge to nowhere in the news recently is a little different. There was a need for it but it had to be an engineering marvel to avoid disrupting a massive stream of traffic. It was designed to be moved suddenly into place with only a brief disruption late one night… It was a fine plan. It made the news. People loved it.

There was one dreadful weakness in the plan however. It was made of reinforced concrete. The marvellous structure was intended to be supported by a column bearing suspension cables and the reinforcements at each end were to be tied into concrete and steel at both ends. Wonderful. Marvellous. It wasn’t installed properly. Recently, a span was put into place and it was left to bake in the sun and shake with traffic moving underneath with no suspension and no tension in the reinforcing steel. That’s a crime. The engineers who planned the installation should be locked up forever for the lives they’ve taken.

Let me be more clear. Concrete is marvellous. It can be shaped smoothly, coloured brightly, made graceful in appearance, and has high compressive strength. Compression happens in the upper member of an “S” beam, which this bridge resembles, as the span sags slightly under its own weight. The crime, however, is that the lower member upon which pedestrians were to walk, is under tension as the bridge sags, not compression. To counter that, the normal procedure is to use steel rods, cables or beams in the lower member to hold everything up. The concrete keeps the steel parts in line. The steel keeps the concrete parts from coming apart. The steel still sags however and must be anchored at both ends and supported from above in this elegant long span. It wasn’t.

So, the span is resting there, shining in the sun, a thing of beauty. Heating, cooling and the rumbling of the traffic causes a crack anywhere in that span and the crack grows, just like in your windshield… Finally, a piece of concrete falls away anywhere along the span. The whole apple-cart is now upset. Steel moves out of position. More concrete crumbles under tension. The thing fails like cloth ripping. Stresses build at the weakest point until the span falls down like it did this afternoon crushing people moving underneath.

Look at the pictures of the scene. Notice the fractured concrete, not at the lower edges but at the upper edges. Under compression when the cracks grew there as the span bent further the concrete disintegrated and the last measure of rigidity exploded in fragments. Hundreds of tons falling several metres is like a horrible mouse-trap, only there were humans underneath. The only thing that saved any was that the lower parts of the bridge fell in chunks around the bending/failing points.

This is a catastrophe. It was totally unnecessary. It was preventable. Multiple people had to make multiple unsound judgments to make it happen. They need to rot in jail if not to be killed. The bridge would have worked as planned if it were made of steel only, not concrete. The bridge would have worked as planned if the reinforcements had been suspended and anchored properly. Instead, lives have been lost, useful technology will be forever linked to disaster, and the life-saving passage across a busy road will be delayed a year or more. How many more will have to die because of this crime?

UPDATE – Here’s a video of the collapse. Early on in the process, the bridge bent/broke at the first reinforcement position on the top side. It needed that suspension. It wasn’t there.

About Robert Pogson

I am a retired teacher in Canada. I taught in the subject areas where I have worked for almost forty years: maths, physics, chemistry and computers. I love hunting, fishing, picking berries and mushrooms, too.

20 Responses to Another Bridge To Nowhere

Oiaohm wrote about trusses. Clearly the truss was insufficient. That theory might have made sense if the truss was tied to the foundation. Nothing prevented anything from moving once it started. I have multiple trusses under my roof not only to bear the load but to distribute and adapt to the load. The FIU bridge was marginal at best. Engineers are required to overbuild rather than trusting to luck.

Grece Well, seeing the actual drawing now https://pbs.twimg.com/media/DYc6_BIU8AAXTV4.jpg:large there should have been a pylon and supports installed before the base was removed. To me, it seems that a installation procedure was not followed, and nothing to do with lightweight / heavyweight concrete or even cracking concrete. When you have a suspension span such as this, you ALWAYS need the supports in place to holder up the camber under load.

Right wrong and missed it. Take a close look a the design you Grece references. Note the triangle internal framing that the suspension connects to. So suspension cables only run to the roof of that bridge in design. There is a internal frame between the roof and floor that people walk on is there to hold the weight of the bridge + the work crew so you don’t need supports under. The load the supports were place above the load by doing a Truss bridge.

The bridge is not a pure suspension bridge. Its a Truss-Suspension hybrid. So it was not a Suspension Span without the Suspension cables it was a Truss span.

Number of people reported hurt the bridge was not loaded far enough that it should have had a issue from the people on the bridge as the numbers on the bridge was less than the numbers of a work crew working on the bridge.

The issues that are common for a failure like this.
1) The concrete mix is the wrong one.
2) The person doing the plans did get the maths right on the truss so it was not in fact strong enough.
3) someone stuffed up assembling the truss parts

There are hybrid bridges in japan that are not complete. The truss section and the tower for suspension is there but suspension cables have never fitted and they have been like that for decades as it was deterred that those bridges would never get filled with enough people to cause issue.

Why are truss-suspension designed liked means when you get to putting in the suspension cables you don’t have to block under it. You should have enough structural strength in Truss part to support work crew and tools to connect and tighten the suspension cables. It also reduces your volume of scaffolding to be removed.

Robert Pogson the hybrid truss-suspension design is no revolutionary either.This not a problem of the strength of concrete. No one puts huge slabs under tension without reinforcement. Not securing reinforcement nullifies it.
The design has enough reinforcement. Also the video to anyone who knows what they are looking at shows a clear truss-suspension design.

Please note I did not say the problem was with the strength of the concrete. One of the possible issues is weight of concrete. Its like the difference between concrete that is 20% zeolite vs a normal mix. The zeolite version is lighter but strength almost the same. Please note mixing zeolite into into concrete makes it resistant to icing over and more general chemical resistance. That is a 15% difference in final mass just with the zeolite.

There are quite a few different mixes that produce a lot of different weights of concrete with the same structural strength. There is something interesting zeolite concrete is not the same color as your normal concrete made from generally sourced sand. All your strong lightweight concretes contain percentages of zeolite.

Carbon Fiber is one the materials you find in light weight concrete aggregate mixes this alters the concrete response to tension.

Making a light weight concrete that is strong is quite a complex mix at times and your structural properties alter a lot. Reality here is amount of reinforcing and support a Concrete needs is directly linked to what mix it is. Yes you can have cases were one mix need reinforcing steel and the other mix does not in the same location all due to what the concrete aggregate is.

DrLoser wrote, “Youâ€™re not a structural engineer, so the basic design of the bridge is entirely beyond you.”

Nonsense. I understand perfectly well what forces like gravity do to concrete and steel. The bridge was well-designed as I see it. The implementation was highly flawed however. There is nothing revolutionary about the design. The world abounds with suspension bridges but they have to be suspended. This one wasn’t. It was left out in the sun to crumble and fall on human beings. That’s a crime.

A relevant but unrelated issue arose in my yard this year. Damned snowmobilers took to crossing my yard without permission. There’s a law against that. However, these bastards were not seen in real time and there are no pictures. I’ve seen machines tooling around without identifying plates. What’s a property-owner to do? I put up barriers to make my property less convenient. People commented that I was risking being sued if one of these geniuses injured themselves trespassing on my property. Compare that “crime” with dropping hundreds of tons of concrete and steel on commuters… I rest my case. It’s the same kind of recklessness if you ignore the astronomical difference in severity.

I don’t wish to diminish the human consequences here, Robert, but at which stage would you have inserted your “unique” expertise?

You’re not a structural engineer, so the basic design of the bridge is entirely beyond you.

You’re not a civil engineer, so the trifling matter of supporting the bridge at both ends, and at points below, is entirely beyond you.

And you’re not a surveyor or an inspector or a regulator or in fact anything of any consequence whatsoever.

Asinine comments, however — that would be your speciality. Trust you to turn a tragedy into an “I could have done better, if only they’d let me” story. Want my opinion? (I know you don’t.) This is either a case of financial peculation, where the construction company cut corners, or else it’s the inevitable consequence of employing a team of under-qualified ignoramuses simply because it’s easy and cheap to employ under-qualified ignoramuses.

Under-qualified and easy and cheap ignoramuses like you, Robert, as you have so amply demonstrated in Saudi, in the Frozen North, and no doubt elsewhere. Get used to it. We live in an imperfect world, and you are a big part of it.

Grece wrote, “When you have a suspension span such as this, you ALWAYS need the supports in place to holder up the camber under load.”

Exactly. I read reports that “cables” were being tightened, so they may have had some crane or such supplying lift but I don’t see that in any of the pictures. It just looks wrong. That the bridge stayed up for days in that state indicates the design/implementation was marginal but with thermal cycling and vibration from traffic and visible cracks disaster loomed. I just can’t forgive folks taking a gamble on others’ lives. There were five lanes of traffic. There could have been dozens killed/maimed, maybe more with a school-bus or two.

This project was wrong in so many ways. I can see that wrongful death suites will abound, workplace safety violations and criminal charges too. Also, that dangerous crossing will persist for pedestrians. I expect it could be five years before the dust settles. Since the engineering community knew of this project and thought it OK, there could be repercussions of a general nature. The professions are supposed to be self-disciplining but when they aren’t regulators/legislators have to do something.

It may not be obvious to motorists travelling on pneumatic tires and springs and shock-absorbers and a cushioned seat but cars travelling along a roadway do shake the earth and everything attached to it. I’ve measured buildings swaying. I’ve felt the vibrations under my feet and heard the rumbles. Leaving an eggshell to span a roadway without proper anchors/suspension is a crime. Experimenting with lives like that is a crime.

Well, seeing the actual drawing now https://pbs.twimg.com/media/DYc6_BIU8AAXTV4.jpg:large there should have been a pylon and supports installed before the base was removed. To me, it seems that a installation procedure was not followed, and nothing to do with lightweight / heavyweight concrete or even cracking concrete. When you have a suspension span such as this, you ALWAYS need the supports in place to holder up the camber under load.

Grece wrote, “I am willing to bet my stash of Canadian Tire Money, that your assessment is totally off base”.

It’s already in the news that cracks were spotted days before the fall but they were dismissed/ignored and the message was sent asynchronously and not followed up. BTW, here’s a good dash-cam video of the crash… The bridge failed at the north end where the cracks were seen… So, not only was the implementation poorly done but the tragedy could have been prevented between the time of the observation of the cracks and the fall. The web of complicity grows. FL DOT needed to man their damned phones. The engineer needed to follow up and get traffic stopped. “Pride cometh before a fall” is still true.

Robert!…why so emotional? I am willing to bet my stash of Canadian Tire Money, that your assessment is totally off base, as is your feeble brain. It must have been a slow day for you and CNN and nothing news worthy to whine about regarding Trump.

Robert Pogson there are many bridges of quite close to the same design in japan that have stood the test of time that have no suspension cables. There is a difference in the concrete used in fact a huge one. The japan ones use light weight concrete mixes comes to about 1/4 of the mass the USA bridge was.

Before getting too upset with the engineering who designed and planned the bridge we need to be sure the concrete was not swapped with the cheaper heavier mixes with worse over all properties. Yes the heavier mixes are slightly stronger compared to the light weight mixes but there is a problem the heavier mixes don’t gain strength as fast as they gain mass this leads to major goofs.

Basically the “It fine we used a stronger concrete instead problem” and forgetting the mass problem. Light weight mixes that are between 1/2 to 1/4 the mass of the stronger concrete have 90-95 percent the strength. Yes gaining 5 to 10 percent strength while doubling to quad the mass kind of does not work.

So it will pay to wait on the report to find out if it was built from the correct concrete. If it the correct concrete as per the plans and the deployment was done how the engineer wrote then the engineer is at fault.

By the way light weight concrete that is not pigmented is different color to your normal concrete and that bridge was made from non pigmented concrete so from the video you can tell its not a lightweight mix.

That’s nice, Bob. There is a bit of difference between you’re piddly weekend home improvement project and a bridge. By the way, where is your outrage over your Progressive Party pushing legislation to require parental consent for teen-abortions in Canada?

Grece missed one important point when he wrote, “Itâ€™s nice to speculate and play arm-chair quarterback, but your ramblings are just that.”

The bridge fell down, killing several innocent people. How do you explain that except some PEs failed miserably to do their jobs? How do you explain that except reinforcement of concrete was not done properly? Done properly, reinforced concrete lasts indefinitely. Proper engineers build in huge margins on yield strength so this kind of thing doesn’t happen. Why didn’t they do that? Did they feel lucky? Were they Trumpists? I’ve built with reinforced concrete. It’s still as good as the first day after decades. This bridge did not last a week and it wasn’t under load at all.

Robert, since when are you a civil engineer with a PE license? In fact, I doubt you have a PE license in any subject matter. It’s nice to speculate and play arm-chair quarterback, but your ramblings are just that.

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